This invention relates to apparatus especially adapted for use in ovens of commercial bakeries for igniting a combustible fuel to produce a flame and for monitoring the presence of the flame.
It is conventional in the baking industry to utilize gas fired bakery ovens which define an enclosure through which baked goods are conveyed by chain or other conveyors which extend longitudinally of the oven. Extending transversely of the path traversed by the conveyor is a plurality of burner tubes which are spaced apart from one another so as to enable the interior of the oven to be heated to desired temperature levels.
Each burner is coupled to a source of combustible fuel, such as natural or propane gas, and each burner is provided with a ribbon or other fuel outlet through which the gas may pass for combustion. At a selected point along the length of each burner is positioned a fuel igniter by means of which fuel flowing through the burner outlet may be ignited.
At one time in the past the fuel igniter was constituted by an electrode positioned adjacent a burner tube at ground potential but spaced from the latter by a gap. The electrode was coupled to an electrical energy source which functioned to generate sufficient energy to enable sparks to jump the gap between the electrode and the burner tube. In the earlier embodiments of such apparatus the sparks were generated continuously, even when the flame was present. The continuous sparking was to ensure that whatever fuel was discharged from the burner would most likely be ignited.
The continuous sparking concept has significant disadvantages. For example, passing sparks continuously through a flame causes the formation of solid carbon xe2x80x9cwhiskersxe2x80x9d which may bridge the spark gap and short the spark. In addition, maintenance of a proper spark gap between the igniter electrode and the burner is difficult due to the expansion and contraction of the burner tubes as they become heated and cooled. Further, heat generated from the constant sparks results in electrode wear and enlargement of the spark gap which leads eventually to loss of the spark.
In those instances in which there is no spark and the burner fails to light, loss of oven heat results, thereby adversely affecting the baked products. In the event of the failure of a burner to light, there is a possibility of creating an unsafe condition due to the introduction of unburned gas into the oven.
Various proposals have been made heretofore to overcome these problems, but none has been able to eliminate the basic flaws of a constant sparking ignition system.
The difficulties with the constant sparking ignition system long have been recognized. One proposal to overcome some of the problems is the provision of solid state, electronic spark ignition/flame rectification proving modules to replace the continuous spark ignition system. The ignition/flame rectification modules provide ignition, thereby establishing a flame, sense the presence of the flame, and discontinue sparking during the presence of the flame. In a system using these modules the presence of a flame disables the generation of sparks, thereby overcoming many of the problems associated with continuous sparking. These modules also function in the absence of the flame at an individual burner to shut off the flow of fuel to the affected burner, thus enhancing safety.
Although the ignition/flame rectification proving module represents a significant advantage over the continuous sparking system, the ignition electrode of such module still remains a problem because of the difficulty in providing and maintaining a proper spark gap between the ignition electrode and the burner.
A principal object of the invention is to provide apparatus for igniting combustible fuel to generate a flame and which overcomes the objectionable characteristics of currently available ignition systems.
Apparatus constructed in accordance with the preferred embodiment of the invention comprises an ignition system which is compatible with the ignition/flame rectification proving modules referred to above, but which eliminates or minimizes some of the problems associated with maintaining the proper spark gap of the spark ignition system. Such apparatus comprises an elongate support formed of dielectric material and through which extends an electrically conductive electrode by means of which sparks may be generated. Also extending through the dielectric support is an electrically conductive electrode terminating at one end in an electrically conductive plate which is positioned adjacent the end of the ignition electrode, but spaced therefrom a distance corresponding to a desired width spark gap. The free end of the plate is bent so as partially to embrace the ignition electrode and to extend somewhat beyond the latter. The bending of the plate enables fuel issuing from the burner tube to be concentrated at the spark gap and the extension of the plate beyond the ignition electrode provides assurance that the ignition electrode will not engage the burner tube, which normally is at ground potential, and short the spark.
The ignition electrode and the ground electrode are secured in the support against rotary movement relative to the support and to one another.